The invention relates to a a loudspeaker comprising:
a magnet unit which generates a magnetic field;
an element suspended for resilient movement round a stable rest position, such as a diaphragm, a cone, a dome or other element suitable for radiating sound with selected properties; and
an electrical conductor, for instance a speech coil, connected to that movable element and having current feed terminals, which conductor is placed in the said magnetic field such that when current is passed through this conductor a force is exerted on the movable element which imparts to the element a displacement from its rest position;
the conductor being covered by a corrosion and oxidation resistant coating such that entry of the gases stimulating corrosion or oxidation of the conductor, particularly oxygen, is prevented.
Such a loudspeaker is generally known.
E.g. from JP-A-59-138 199 an electro dynamic loudspeaker is known, in which all faces of exposed parts of the diaphragm, the preferable support section, a coil bobbin, the voice coil and adhesive of the coupling section are covered with a synthetic resin layer. In connection with this prior art technique it should be noted that in this prior art loudspeaker also parts not subjected to high temperatures are coated. Such coating only contributes to the weight of the movable structure, affecting the sensitivity of the loudspeaker.
From U.S. Pat. No. 3,935,402 a loudspeaker voice coil arrangement is known in which the aluminum voice coil wire is provided with a flexible anodized coating. Anodization does generally not provide a sufficient insulating value and is susceptible to damage during the winding of the voice coil.
EP-A-0 112 559 discloses a loudspeaker having a cilindrical voice coil specifically adapted for automatic production. The flexible feed terminals are designed as flat strip conductors connected with a synthetic resin support strip. The exposed faces of the conductor strips are covered with a polyimide-coating foil. The voice coil is manufactured according to general prior art standards.
U.S. Pat. No. 4,479,035 discloses a loudspeaker assembly having a voice coil bobbin formed out of a high temperature ceramic material. The helical transducer windings are formed of a molybdenum-mangane metallization. Specifically under high temperature conditions these windings may be susceptible to oxidation or, in general, corrosion.
It is a purpose of the invention to provide a loudspeaker, in which the conductor, generally consisting of aluminum, is not susceptible to oxidation and corrosion, not even at the highly increased temperatures that can occur in a loudspeaker. It is furthermore a purpose of the invention to design the loudspeaker in a way such that the sensitivity of the loudspeaker is not to any substantial degree decreased, due to the fact that the mass added by the protected measures to the movable parts, is negligible.